62 THE INORGANIC CONSTITUENTS OF MARINE INVERTEBRATES. 



for more than many smaller alcyonarians in the formation of magnesian limestone. If, how- 

 ever, the warm-water organisms are as abundant as the cold-water forms, and if their aggre- 

 gate mass is as great, then the tropical limestones of marine origin should be more richly magne- 

 sian than those from higher latitudes. The determination of the facts we must leave to 

 zoologists. 



In conclusion we must express our thanks to the officers of the United States National 

 Museum and the United States Geological Survey, who have aided us by furnishing authentic 

 material for our investigations. Messrs. Paul Bartsch, Austin H. Clark, William H. Dall, 

 W. L. Schmitt, T. Wayland Vaughan, and Frank Springer and Miss M. G. Rathbun have all been 

 most generous with their services. Dr. Marshall A. Howe, of the New York Botanical Garden, 

 has also been most kind in supplying us with algse, and Prof. L. R. Gary has kindly furnished 

 us with valuable unpublished analyses. Without the help of these friends our research would 

 have been impossible. 



Addendum. — Since the manuscript of this paper was prepared Prof. A. G. Mayor *" has 

 published an important paper on Rose Atoll, near Samoa. The reef here consists chiefly of 

 Lithothamnium remains, with very little coral. Analyses of the reef rock by A. H. Phillips 

 gave percentages of magnesium carbonate ranging from 14.36 to 19.47. 



»» Am. Fhilos. Soc. Proc, vol. 60, p. 62, 1921. 



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